As you can see, the labels on the static box have a white background, which looks pretty terrible, but the main problem is that they are overlapped by the box's contents. This is despite adding spacers to the sizer, which seems to have no effect on Windows.

I just realised I was wrong that the spacers have no effect. I've "fixed" the problem by being extremely liberal with my use of padding. If I were to remove the spacers completely, it would look very broken.